Method for controlling ventilation flow rate in a container and a container being controlable by the method

Abstract

A method for controlling a ventilation flow rate of a refrigerated cargo storage space with a refrigeration unit comprising one or more evaporator fans arranged to drive ventilation flow across an evaporator and into the space. The method comprises operating the fan(s) at a first speed, determining a measure of the pressure difference across the fan(s) when the fan(s) are operated at said first speed, selecting an operational speed of the fan(s) based on the measure and a predetermined limit value for said measure, the operational speed a first predetermined speed in case the measure of the pressure difference is lower than a limit value for said measure of the pressure difference, and a second speed in case the measure of the pressure difference is higher than the limit value for the measure, the second speed lower than the first speed, and operating the fan(s) at the selected operational speed.

What is claimed is: 
     
         1 . A method for controlling a ventilation flow rate of a cargo storage space in a container, wherein a refrigeration unit is provided for refrigeration of the cargo storage space, the refrigeration unit comprising one or more evaporator fans being arranged to drive a ventilation flow from the cargo storage space, across an evaporator of the refrigeration unit and into the cargo storage space, wherein the ventilation flow rate is controlled by controlling the speed of the evaporator fan(s), the method comprising the steps of:
 operating the evaporator fan(s) at a first speed,   determining a measure of the pressure difference across the evaporator fan(s) when the evaporator fan(s) are operated at said first speed,   selecting an operational speed of the evaporator fan(s) based on the determined measure of the pressure difference and a predetermined limit value for said measure, wherein the operational speed is a first predetermined speed in case the determined measure of the pressure difference is lower than a limit value for said measure of the pressure difference, and a second speed in case the determined measure of the pressure difference is higher than the limit value for the determined measure, wherein the second speed is lower than the first predetermined speed, and   operating the evaporator fan(s) at the selected operational speed.   
     
     
         2 . The method according to  claim 1 , wherein the first predetermined speed is the maximum speed of the evaporator fan(s). 
     
     
         3 . The method according to  claim 1 , wherein the method, provided that the second speed is selected, further comprises the steps of determining a measure of the pressure difference (ΔP) across the evaporator fan(s), and
 adjusting the operational speed of the evaporator fan(s) in order to reach a predetermined set point value for the determined measure of the pressure difference across the evaporator fan(s). 
 
     
     
         4 . The method according to  claim 1 , wherein the cargo storage space contains stored commodities, and wherein the predetermined limit value for said measure has been predetermined for that commodity. 
     
     
         5 . The method according to  claim 4 , wherein the predetermined set point value for the determined measure of the pressure difference across the evaporator fan(s) has been predetermined for that commodity. 
     
     
         6 . The method according to  claim 5 , wherein a control unit for controlling the ventilation flow rate by controlling the speed of the evaporator fan(s) receives data pertaining to the commodity, and wherein the predetermined set point value for the determined measure of the pressure difference across the evaporator fan(s) is included in or derived from said received data. 
     
     
         7 . The method according to  claim 6 , wherein the received data comprises identification of the type of commodity and the step of deriving the predetermined set point value for the determined measure of the pressure difference across the evaporator fan(s) comprises a look-up in predefined values stored in the control unit or at an external data storage with which the control unit is enabled to communicate. 
     
     
         8 . The method according to  claim 1 , wherein each evaporator fan comprises a variable speed electric motor arranged to drive the evaporator fan and an electric power converter to feed power to the variable speed electric motor. 
     
     
         9 . The method according to  claim 1 , wherein external warning information is issued in case the determined measure of the pressure difference is lower than the limit value for said measure of the pressure difference. 
     
     
         10 . The method according to  claim 1 , wherein the refrigeration unit is operated to achieve and maintain a set point temperature of the cargo storage space, wherein the cargo storage space contains stored commodities and the set point temperature of the cargo storage space is within the range of −5° C. to 30° C., and wherein the stored commodities produces respiration heat at the set point temperature of the cargo storage space. 
     
     
         11 . The method according to  claim 1 , wherein the container is an intermodal refrigerated container. 
     
     
         12 . The method according to  claim 1 , wherein the refrigeration unit is an integrated refrigeration unit in the container. 
     
     
         13 . The method according to  claim 1 , wherein the refrigeration unit comprises a compressor, a condenser and an expansion valve. 
     
     
         14 . An intermodal refrigerated container comprising an integrated refrigeration unit for refrigeration of a cargo storage space of the container, the integrated refrigeration unit comprising a compressor, a condenser, an expansion valve, an evaporator and at least one evaporator fan, which is arranged to drive a ventilation flow from the cargo storage space, across the evaporator and into the cargo storage space, and a variable speed electric motor arranged to drive the evaporator fan(s),
 wherein the intermodal refrigerated container comprises a control unit for controlling the ventilation flow rate by controlling the speed of the evaporator fan(s), the control unit being adapted to perform the steps according to  claim 1 .